The plan can be activated free of charge when signing up for Dropshare Cloud using the Setapp version of the Dropshare app. It will not work when signing up in a web browser.
Step by step instructions
Select "Dropshare Cloud" in the introduction wizard, or open the preferences, select "Connections" and add a new connection from there. Make sure the Setapp icon is visible in this screen. This is only the case for the Setapp version of the app.
In the next screen, click on "Sign Up" to create a new account with Dropshare Cloud that is eligible to redeem the complimentary subscription.
Follow the instructions to sign up. When done and your account is activated, you are automatically subscribed to the complimentary Setapp plan.